This invention relates generally to apparatus for fusing a toner image to a support. More particularly this invention relates to fuser apparatus including a fuser member which contacts a toner image carrying support inclined to the horizontal transversely to the direction of movement of the support and further including wick means for applying to the fuser member. The wick means includes means for retarding migration of release material along said wick means due to the influence of gravity.
In electrophotography a light image of an original is projected upon a charged photoconductive member to form a latent electrostatic image corresponding to the original. A visible toner image is produced by developing the electrostatic image with charged toner particles. If the photoconductive member is reusable in the form of a belt or a drum, the toner image is then transferred to a support such as a web or sheet of plain paper and fused to the support. If the photoconductive member itself is the support then the toner image is fused directly to the photoconductive member.
One technique used to fuse a toner image to a support is through the application of heat and pressure by contacting the toner image with a heated fuser member such as a roller or belt. For example, a pair of rollers held together under pressure form a nip through which a toner image-carrying support is passed. One or both of the rollers are heated to melt the heat-softenable toner particles to fuse the toner image. In such fusers at least one of the rollers may be formed with an elastomeric layer to lengthen the nip through which the toner image passes in order to increase fusing time and to lower fusing energy requirements. Commonly used elastomers (e.g. silicone elastomer or fluoroelastomer) are those which are resistant to degradation at high temperatures over a long operating life and which have good release properties to prevent offset of toner particles to the surface of the fusing member and to obviate the tendency of a support to stick to the fuser member.
In order to enhance the release properties of the fuser a coating of release material such as silicone release oil may be applied to the fuser member by means of a wick which has a segment in contact with the effective fusing length of the member. The wick may be made of a high-temperature resistant felt such as the nylon, Nomex.RTM.. The wick may be saturated with release material which is gradually applied to the fusing surface of the fusing member over a period of time. Alternatively, the wick may be supplied with release material from a separate reservoir on a demand basis during operation of the electrographic apparatus. Since electrographic apparatus generally have a support path which is transversely horizontal to the direction of movement of a support along the path, there is no tendency due to the influence of gravity for release material to migrate laterally along the length of the wick and to build up at one end. In certain apparatus, the support path is transversely inclined to the horizontal. Thus, the KODAK STARVUE Microfilm Reader-Printer Apparatus is inclined to the horizontal for operator convenience and ease of operation. An electrographic printer used in such apparatus would also be inclined to the horizontal and have a support path transversely inclined to the horizontal. Where release material which is fluid at fusing temperatures is applied to a fuser member adjacent to such a transversely inclined path, there is a tendency due to gravity for release material to migrate laterally toward the lower end of the wick thus creating an excess of release material along the lower end of the wick and an insufficiency of release material along the upper end of the wick. This causes excess release material to be carried off by a support on one side of the sheet path and toner and/or the support to be stuck to the fuser member on the other side of the path.
Thus, it would be desirable to provide fuser apparatus for use in electrographic apparatus having a support path transversely inclined to the horizontal in which release material is evenly applied to the effective fusing length of the fusing member so as to avoid excessive application of release material at the lower end of the fusing apparatus and insufficient application of release material at the upper end of the fusing member.